This invention relates to compositions of matter, methods, and apparatuses useful in producing stable high solids colloidal silica and uses thereof. As described in U.S. Pat. Nos. 6,486,216, 6,361,653, 5,840,158, 6,361,652, 6,372,805, and US Published Patent Application 2011/0250341 A1, Colloidal silicas, are aqueous systems with silica microparticles suspended within them. Colloidal silicas have been found to be useful in numerous fields of application dependent on the particle size including the manufacture of silicon wafers and carbonless papers, as anti-soilants, lubricants, high temperature binders, abrasives, moisture absorbers, and abrasion resisters. In particular as described for example in U.S. Pat. Nos. 4,753,710, 4,913,775, 4,388,150, 4,385,961, 5,182,062, and 5,098,520, colloidal silicas have been found to have an especially useful number of applications in the papermaking industry, especially in enhancing the retention and drainage of paper pulps.
The nature of colloidal silicas unfortunately subjects them to a number of limiting constraints. When dosing a colloidal silica two factors are of large significance, average particle size (usually measured in surface area) and the percentage of the aqueous system that the particles comprise (solids %). For a given application there is an ideal particle size at which the colloidal silica will be most effective. Often a user would prefer to apply as high a solids % at that particle size as possible. However applying that ideal particle size is often impractical because the colloidal silica is not stable at that size at a high solids % for a sufficient length of time.
Stability of colloidal silicas is very important. If the colloids are not stable they can only be used during a very narrow window of time. This narrowness forces numerous costs and inconveniences on users in terms of among other things: storage costs, preparation costs, equipment requirements, and the need to constantly replace no longer stable colloids. The stability of colloidal silica is inversely proportional to both solids % and to particle size. As a result a silica colloid of a given particle size will only be stable for a significant period of time (for example >3-6 months) up to a particular solids % which is usually lower than the ideal amount. When a colloid's solids % exceeds that level, the silanol groups on various microparticles interact with each other and form interlocked complexes which cause the aqueous system to become a highly viscous sludge which is no longer effective for its intended use. In addition, other factors can impair the stability of the microparticles. As a result users are often forced to choose between more stable colloidal silicas that have a lower solids % than they want or they must use colloidal silicas having a desired solids % but which are less stable than desirable.
Thus there is a clear need for and utility in an improved method of producing stable high solids colloidal silica. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. § 1.56(a) exists.